A local interconnect network (LIN) is a specification for a serial communication system and, consequently, for a serial bus system, which is also called a LIN bus. This bus system may be used for achieving communication between sensors and/or actuators and a control unit as users of the bus system, e.g., in a motor vehicle.
Event-triggered frames (ETF) and sporadic frames (SF) are introduced by the LIN 2.0 standard for data that are transmitted between the users. Therefore, it is possible to influence a time schedule (schedule) for transmitting data, that is, the above-mentioned frames allow sporadic or event-driven data transmission, but the frames themselves are rigidly defined in the schedule.
In sporadic frames, a plurality of messages having static priority may be defined for a time slot. In such a time slot (slot), a message is only sent when data are present for a master as a user of the bus system, or when slave responses are demanded by the master. If neither is the case, then the bus system remains empty during this time. Thus, the bus system cannot be utilized to full capacity, using sporadic frames.
Using event-triggered frames, it may be taken into account that not all slaves, as users of the bus system, have data to send in every data transmission cycle. In this context, an event-triggered frame may be assigned a plurality of slaves, that is, a plurality of slaves may respond to a header of an event-triggered frame. If there is a collision between transmitted frames, then the slaves may detect this by reading back the data, and may interrupt the transmission process. The master then detects a receiving or timeout error. At a next time slot of this event-triggered frame, the master interrogates the slaves, using normal messages, or using separate identifiers. That is, for each slave that reacts to an event-triggered frame, in each instance, an unequivocal, normal identifier must also exist.
As of the LIN 2.1 standard, it is stipulated that after a collision, the master must change one time to another time schedule that is collision-free, and after it is finished, the master must switch back again to the original table of the time schedule. To this end, however, it is necessary that collision detection is implemented. In addition, in the event of a collision, considerable delays are created by the repeated and individual interrogation of the slaves. Thus, as a rule, event-triggered frames are only useful when only very few collisions are to be expected.
A control method for media access in a serial bus is described in German Patent Application No. DE 197 21 740 A1. This serial bus includes several users that communicate with one another via data messages. In order to allow individual users to access the bus at particular times, trigger messages are sent in a cyclical sequence by a first user taking the form of a master. In this context, each trigger message contains the beginning and the duration of the sending authorization for at least one user selected by the master. For the selected users, a timing interval for transmitting data messages is stipulated by the trigger message. Prior to the sending of a next trigger message, the slaves may request, from the master, sending authorizations for further data messages.